1. Technical Field
The present invention relates to a lithium ion secondary battery and, more particularly, to a lithium ion secondary battery having separate battery accessories coupled on a cap plate of a bare cell.
2. Related Art
Typically, secondary batteries can be charged/discharged numerous times in comparison with conventional primary batteries that cannot be charged. Currently, Ni-MH batteries, Li batteries, and Li-ion batteries are usually adopted as a secondary battery.
The secondary battery can be classified into a liquid electrolyte battery and a polymer electrolyte battery based on the electrolyte used in the battery. In the art, a battery using liquid electrolyte is called a lithium ion battery, and a battery using polymer electrolyte is called a lithium polymer battery. In addition, the lithium ion battery has been manufactured in various shapes, such as cylindrical, rectangular, and pouch shapes.
Flammability of the lithium secondary battery has been reduced by using a carbon based electrode instead of metal. However, safety has been still important in the manufacturing process of the lithium secondary battery because of the flammability of anhydrous electrolyte and the high energy density of the lithium.
Furthermore, in the lithium secondary battery, when over-discharge happens, battery components such as a negative electrode charge collector are damaged so that the battery becomes no longer rechargeable. Therefore, atypical lithium secondary battery is manufactured by combining a bare cell having a basic battery structure for charge/discharge operations and a protection circuit or unit for preventing overcharging, overdischarge, overheating, or overcurrent. The protection circuit or unit may be physically and electrically connected to the bare cell in the shape of a printed circuit board or an accessory at a side surface, upper surface or lower surface of the bare cell.
When a cylindrical canned battery is used, the cap assembly of the bare cell naturally has a function of preventing overheating or overcurrent. However, when a rectangular canned battery is used, the cap plate does not have such a safety function. Therefore, in the rectangular can, the bare cell and a separate safety device must be used together. In recent years, the safety device or unit, such as a protection circuit board in the rectangular can, is frequently mounted on an upper surface of the cap plate.
On the other hand, when a packaged battery in which a plurality of bare cells are combined with one another is used, an additional accessory, such as a cap cover, may be provided on the cap plate in order to connect the bare cells with one another in the package, or to connect a protection circuit to them. In this case, the cap cover itself does not provide a safety function, but it is just an accessory for electrically connecting components which can be formed in various shapes according to the interconnection of the bare cells. A peripheral region of the cap cover is usually made of a resin material so as to provide a support or a mount that makes contact with the bare cell. In the center of the cap cover, metallic terminals connected to the electrode terminals of the bare cells and the protection circuit, and a conductive interconnection for connecting the metallic terminals, maybe provided. Otherwise, the metallic terminal may be formed in a wider area without a separate interconnection.
The protection circuit may not be directly provided in an upper portion of the cap assembly. Instead, the protection circuit may be provided on the cap assembly with battery accessories, such as a washer for preventing a lead line connected to the electrode terminal in an upper portion of the cap assembly from making contact with the cap plate in other portions.
However, in the cap assembly forming an upper portion of the rectangular can, electrode terminals which are electrically separated from the cap plate extend from the upper surface of the cap plate. Accordingly, it is difficult to safely combine battery accessory assemblies with the cap assembly, for example, by robustly mounting a battery accessory assembly on the cap assembly or temporarily place the assembly and then welding it. Furthermore, since there is no means for guiding correct positions of the battery accessories around the cap assembly, it is not easy to place the accessories in their correct positions. If the accessories are not placed in their correct positions, the electrical connection between accessories and the bare cells may also be unstable. In this case, if the accessories are temporarily attached to the cap plate and then fixed by, for example, adhesion or welding, electrical connection between them may also be unstable and dangerous.
Conventionally, there have been difficulties in manufacturing the package battery because, for example, it has been difficult to fix the cap cover despite the fact that the cap cover should be fixed on an upper portion of the cap plate of the bare cell when the cap cover is used in the packaged battery.
Also, there is no part for stabilizing a washer when the washer is installed in on the cap plate, and the washer may be easily removed from the upper portion of the cap assembly by an external impact.